The discovery that metallocenes of transition metals can be used as catalysts for the polymerization of olefins has led to significant amounts of research since it was found that different metallocenes could produce different types of polymers. One of the earliest references to the use of metallocenes in the polymerization of olefins is U.S. Pat. No. 2,827,446 which discloses a homogeneous, i.e. liquid, catalyst system of bis(cyclopentadienyl) titanium dichloride and an alkyl aluminum compound. The activity of such systems was not, however, as high as would be desired. It was latter discovered that more active catalyst systems would result if the metallocene was employed with an alkylaluminoxane cocatalyst, such as that disclosed in U.S. Pat. No. 3,242,099.
U.S. Pat. Nos. 5,498,581 and 5,565,592 revealed a particularly interesting class of new metallocenes that are suitable for use in the polymerization of olefins, namely bridged metallocenes having a terminally unsaturated group extending from the bridge. One particularly preferred metallocene of that type was the metallocene which can be called 1-(9-fluorenyl)-1-(cyclopentadienyl)-1-(methyl)-1-(but-3-enyl) methane zirconium dichloride. The metallocenes of that type were found to be particularly desirable in that they allowed for the production of solid catalyst systems that could be employed effectively in slurry polymerization processes.
The present invention is based on the subsequent discovery that metallocenes which have a bridge with a terminally unsaturated group and also an aryl substituent on the bridge produce unexpected benefits.